Organ development requires a tightly controlled program of cell proliferation followed by growth arrest and differentiation and, often, programmed cell death. The balance between the number of cell divisions and the extent of subsequent programmed cell death determines the final size of an organ (reviewed by Bryant and Simpson, Quart. Rev. of Biol., 59:387-415 (1984); Raft, Nature, 356:397-400 (1992)). Although much of the cellular machinery that determines the timing of onset and cessation of cell division per se is well understood (reviewed by Hunter and Pines, Cell, 79:573-582 (1994); Morgan, Nature, 374:131-134 (1995); Weinberg, Cell, 81:323-330 (1995)), little is known about the signals that cause discrete groups of cells and organs to terminate growth at the appropriate cell number and size. A better understanding of the signals involved provides possible targets for manipulating the cellular machinery resulting in therapeutic benefits for a number of conditions.
The present invention is based on the discovery that nitric oxide (NO) is an important growth regulator in an intact developing organism. In particular, the present invention relates to a method of increasing in a mammal a population of hematopoietic cells (e.g., hematopoietic stem cells), including precursors to myeloid, lymphoid and erythroid cells, which are capable of undergoing normal hematopoiesis, differentiation and maturation in hematopoietic tissue, wherein the hematopoietic tissue is contacted with at least one inhibitor of NO, such as one or more inhibitors of nitric oxide synthase (NOS), thereby producing hematopoietic tissue having an increased population of hematopoietic stem cells which are capable of undergoing normal hematopoiesis, differentiation and maturation. In one embodiment, the present invention relates to a method of increasing in a mammal a population of hematopoietic stem cells which are capable of undergoing normal hematopoiesis, differentiation and maturation in hematopoietic tissue, comprising contacting the hematopoietic tissue with two inhibitors of nitric oxide synthase, thereby producing hematopoietic tissue having an increased population of hematopoietic stem cells which are capable of undergoing normal hematopoiesis, differentiation and maturation. The method can be carried out in vivo or ex vivo. In addition, the method can be used to prevent differentiation of erythroid cells and/or myeloid cells in the mammal. The method can further comprise contacting the hematopoietic tissue with at least one agent (e.g., a hematopoietic growth factor) which induces differentiation of a selected hematopoietic stem cell population.
The present invention also relates to a method for treating a mammal to increase a population of hematopoietic stem cells which are capable of undergoing normal hematopoiesis, differentiation and maturation in hematopoietic tissue of the mammal. In the method, the hematopoietic tissue of the mammal is contacted with at least one inhibitor of NOS, thereby producing hematopoietic tissue having an increased population of hematopoietic stem cells which are capable of undergoing normal hematopoiesis, differentiation and maturation. In one embodiment, the present invention relates to a method for treating a mammal to increase a population of hematopoietic stem cells which are capable of undergoing normal hematopoiesis, differentiation and maturation in hematopoietic tissue of the mammal, comprising contacting the hematopoietic tissue of the mammal with two inhibitors of nitric oxide synthase, thereby producing hematopoietic tissue having an increased population of hematopoietic stem cells which are capable of undergoing normal hematopoiesis, differentiation and maturation. The method can further comprise contacting the hematopoietic tissue with at least one agent which induces differentiation of a selected hematopoietic stem cell population.
In one embodiment of the method for treating a mammal to increase a population of hematopoietic stem cells which are capable of undergoing normal hematopoiesis, differentiation and maturation in hematopoietic tissue of the mammal, hematopoietic tissue which is to be transplanted is obtained, wherein the hematopoietic tissue to be transplanted can be obtained from the mammal being treated (autologous transplantation) or from another mammal (heterologous transplantation). The hematopoietic tissue to be transplanted is contacted with at least one inhibitor of NOS. The hematopoietic tissue which is to be transplanted is transplanted into the mammal being treated, thereby providing the mammal with hematopoietic tissue having an increased population of hematopoietic stem cells which are capable of undergoing normal hematopoiesis, differentiation and maturation. In one embodiment, two NOS inhibitors are used. The method can further comprise treating the mammal with an inhibitor(s) of NOS before or after transplanting the hematopoietic tissue. Alternatively, the method can further comprise treating the mammal with an enhancer (one or more) of NOS before or after transplanting the hematopoietic tissue.
The present invention also relates to a method of increasing a population of progenitor blood cells (e.g., red blood cells, white blood cells) which are capable of undergoing normal hematopoiesis, differentiation and maturation comprising contacting progenitor cells (stem cells) of blood with at least one inhibitor of NO (e.g., an inhibitor of NOS). In one embodiment, the progenitor blood is contacted with two inhibitors of NOS.
The present invention also relates to a method of increasing a population of dividing cells in a tissue of a mammal comprising contacting the cells with at least one inhibitor of nitric oxide. In one embodiment, the present invention also relates to a method of increasing a population of cells in S phase in a tissue of a mammal, comprising contacting the tissue with an inhibitor of NO, such as an inhibitor of NOS. In one embodiment, the method results in an increase in the size of an organ in which the tissue is occurs. Furthermore, as described herein the cells in S phase can be used in gene therapy.
The present invention also relates to a method of decreasing a population of cells in S phase in a tissue of a mammal and inducing differentiation of the cells, comprising contacting the tissue with an enhancer(s) of NO, such as an enhancer of NOS. In one embodiment, the method results in a decrease in the size of an organ with which the tissue is associated.
The present invention also relates to a method of coordinating developmental decisions of a cell type in a mammal, comprising introducing NO into the cell type or a precursor of the cell type, thereby inhibiting proliferation of the cell type or a precursor of the cell type and inducing differentiation of the cell type or a precursor of the cell type.
A method of inducing differentiation in a mammalian cell population comprising contacting the cell population with NO or a NO enhancer is also encompassed by the present invention.
The invention also pertains to a method of regenerating tissue in an adult mammal comprising contacting a selected tissue (e.g., blood, skin, bone and digestive epithelium), or precursor cells of the selected tissue, with at least one inhibitor of NO, thereby inhibiting differentiation and inducing proliferation of cells of the tissue, then contacting the selected tissue with a compound (e.g., nitric oxide, a growth factor or a combination of both) which inhibits proliferation and induced differentiation. In one embodiment, the method involves repopulating an organ or tissue (e.g., muscle or nerve fiber) comprised of normally nondividing cells by contacting a selected organ or tissue, or precursor cells of the selected organ or tissue, with an inhibitor of NO, thereby inhibiting differentiation and inducing proliferation of cells of the organ or tissue, then contacting the selected organ or tissue with a compound which inhibits proliferation and induced differentiation.
The invention also encompasses a method of producing a subpopulation of hematopoietic cells. In the method, hematopoietic tissue is contacted with at least one inhibitor of NOS, thereby producing hematopoietic tissue having an increased population of hematopoietic stem cells which are capable of undergoing normal hematopoiesis, differentiation and maturation; and at least one agent (e.g., a hematopoietic growth factor) selected to induce specific differentiation of the hematopoietic stem cell population, thereby producing a subpopulation of hematopoietic cells. In a particular embodiment, the hematopoietic tissue is contacted with two inhibitors of NOS.
Identification of NO as an important growth regulator in an organism provides for various therapeutic applications in humans and other mammals.
Results of the work described herein have shown that a transcellular messenger (nitric oxide (NO)) plays a critical role in tissue differentiation and organism development. NO regulates the balance between cell proliferation and cell differentiation in the intact developing organism. Increased production of NO permits cessation of cell division and subsequent differentiation of cell in a tissue, whereas removal of the NO-mediated growth arrest promotes cell division.
Accordingly, the present invention relates to a method of increasing in a mammal a population of hematopoietic cells (e.g., hematopoietic stem cells), including precursors to myeloid, lymphoid and erythroid cells, which are capable of undergoing normal hematopoiesis, differentiation and maturation in hematopoietic tissue, by contacting the hematopoietic tissue with at least one inhibitor (one or more) of NO, such as an inhibitor of NOS. As defined herein xe2x80x9chematopoietic tissuexe2x80x9d is tissue involved in hematopoiesis. e.g., bone marrow, peripheral blood, umbilical cord vein blood, fetal liver, and long term hematopoietic cell culture.
The present invention includes a method for treating a mammal to increase a population of hematopoietic stem cells which are capable of undergoing normal hematopoiesis, differentiation and maturation in hematopoietic tissue of the mammal, in which the hematopoietic tissue of the mammal is contacted with at least one inhibitor of NOS. The invention also pertains to a method of producing a subpopulation of hematopoietic cells by contacting hematopoietic tissue with at least one inhibitor of NOS, thereby producing hematopoietic tissue having an increased population of hematopoietic stem cells which are capable of undergoing normal hematopoiesis, differentiation and maturation; and at least one agent selected to induce specific differentiation of the hematopoietic stem cell population, thereby producing a subpopulation of hematopoietic cells. In a particular embodiment, two inhibitors of NO, such as two inhibitors of NOS, are used in the methods. For example, a combination of L-NAME and ETU can be contacted with the hematopoietic tissue to increase a population of hematopoietic stem cells in a mammal, to treat a mammal to increase a population of hematopoietic stem cells in hematopoietic tissue in a mammal or to produce a subpopulation of hematopoietic cells.
The present invention also relates to a method of increasing a population of progenitor blood cells comprising contacting progenitor cells of blood with at least one inhibitor (one or more) of NO (e.g., inhibitor of NOS). In one embodiment, the present invention relates to a method of increasing a population of progenitor blood cells comprising contacting progenitor cells of blood with two inhibitors of NOS. The sources of progenitor cells of blood include, for example, bone marrow, peripheral blood, umbilical cord vein blood, fetal liver, and long term hematopoietic cell culture. Using the method of the present invention red blood cells and white blood cells (e.g., granulocytes (neutrophils, basophils, eosinophils), monocytes, lymphocytes) can be increased.
The present invention also relates to a method of increasing a population of dividing cells in a tissue of a mammal comprising contacting the cells with at least one inhibitor of NO. In one embodiment, the present invention can also be used to increase a population of cells (targeted cells) in S phase in a tissue of a mammal relative to a similar tissue in an untreated mammal, by contacting the tissue with at least one inhibitor of NO, such as an inhibitor of NOS. In one embodiment, the method results in an increase in the size of an organ with which the tissue is associated. Conversely, the present invention can also be used to decrease a population of cells in S phase in a tissue of a mammal and inducing differentiation of the cells, comprising contacting the tissue with at least one enhancer of NO, such as an enhancer of NOS. In one embodiment, the method results in a decrease in the size of an organ with which the tissue is associated. Furthermore, as described herein the cells in S phase can be used in gene therapy.
The present invention also relates to a method of coordinating developmental decisions of a cell type in a mammal, comprising introducing NO into the cell type or a precursor of the cell type, thereby inhibiting proliferation of the cell type or a precursor of the cell type and inducing differentiation of the cell type or a precursor of the cell type. A method of inducing differentiation in a mammalian cell population comprising contacting the cell population with NO or a NO enhancer is also encompassed by the present invention.
The invention also pertains to a method of regenerating tissue in an adult mammal. The method comprises contacting a selected tissue with at least one inhibitor of NO, thereby inhibiting differentiation and inducing proliferation of cells of the tissue, then contacting the selected tissue with a compound which inhibits proliferation and induces differentiation of the proliferated cells to cells characteristic of the tissue. In one embodiment, the method involves repopulating an organ or tissue (e.g., muscle or nerve fiber) having normally nondividing cells comprising contacting a selected organ or tissue with an inhibitor(s) of NO, thereby inhibiting differentiation and inducing proliferation of cells of the organ or tissue, then contacting the selected organ or tissue with a compound which inhibits proliferation and induces differentiation of the proliferated cells to cells characteristic of the organ or tissue. Compounds which inhibit proliferation and induce differentiation include NO, an enhancer of NO and a growth factor. One or more these compounds can be used to inhibit proliferation and induce differentiation.
Tissue which can be regenerated using the methods described herein include blood, skin, bone and digestive epithelium, nerve fiber, muscle, cartilage, fat or adipose tissue, bone marrow stroma and tendons.
The methods described herein can further comprise the step of contacting the hematopoietic tissue target cells (e.g., bone marrow) with at least one agent which induces differentiation of a selected hematopoietic stem cell population to a particular cell type (e.g., erythrocytes, macrophages, lymphocytes, neutrophils and platelets). For example, in the embodiment wherein a mammal is treated to increase a population of hematopoietic stem cells in the hematopoietic tissue of the mammal by contacting the hematopoietic tissue of the mammal with an inhibitor of NOS, the increased population of hematopoietic tissue can be contacted with an agent, such as a hematopoietic growth factor, which will cause or promote differentiation of the cells of a particular cell type. Agents (e.g., such as hemopoietic growth factors) which can be used in the methods of the present invention to induce differentiation of the increased or expanded number of cells produced by contacting cells with a NOS inhibitor include, for example, erythropoietin, G-CSF, GM-CSF and interleukins such as IL-1, IL-2, IL-3 and IL-6. Alternatively, the methods described herein can further comprise the step of contacting the hematopoietic tissue with at least one agent which further induces or maintains proliferation of the selected hematopoietic stem cell population to a particular cell type (e.g., erythrocytes, macrophages, lymphocytes, neutrophils and platelets).
Inhibitors of NO for use in the present invention include, for example, NO scavengers such as 2-phenyl-4,4,5,5-tetraethylimidazoline-1-oxyl-3-oxide (PTIO), 2-(4-carboxyphenyl)-4,4,5,5-tetraethylimidazoline-1-oxyl-3-oxide (Carboxy-PTIO) and N-methyl-D-glucamine dithiocarbamate (MGD); and NOS inhibitors such as N-nitro-L-arginine methyl-ester (L-NAME), N-monomethyl-L-arginine (L-NMMA), 2-ethyl-2-thiopseudourea (ETU,), 2-methylisothiourea (SMT), 7-nitroindazole, aminoguanidine hemisulfate and diphenyleneiodonium (DPI).
In the methods of the present invention, at least one inhibitor of NO (e.g., NOS inhibitors) can be used. When more than one inhibitor is used in the methods of the present invention, the inhibitors can be the same or different. In a particular embodiment, two inhibitors of NO, such as two inhibitors of NOS (e.g., L-NAME and ETU), are used in the methods of the present invention.
Furthermore, in the methods of the present invention, the NO inhibitor(s) can be administered in a single dose or in multiple doses. The multiple doses can be administered in a day or over a period of days (e.g., a period of about 2 days to a period of about 15 days). For example, the NO inhibitor(s) can be administered over 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or 15 days. In one embodiment, a mixture of two NO inhibitors (e.g., L-NAME and ETU) are administered to the mammal or contacted with the cells twice a day for 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or 15 days. In a particular embodiment, L-NAME and ETU are administered to the mammal or contacted with the cells twice a day for 9 days.
In the methods of the present invention, one or more enhancers of NO can be used. Enhancers of NO include, for example, NOS enhancers, and NO donors such as sodium nitroprusside (SNP), S-nitroso-N-acetylpenicillamine (SNAP), S-nitrosoglutathione (SNOG, GSNO), diethylamine NONOate (DEA/NO), DETA/NO (NOC-18), 3-morpholinosydnonimine (SIN-1) and spermine NONOate (Sper/NO).
NO is a diffusible multifunctional second messenger that has been implicated in numerous physiological functions in mammals, ranging from dilation of blood vessels to immune response and potentiation of synaptic transmission (Bredt and Snyder, Annu. Rev. Biochem., 63:175-195 (1994); Nathan and Xie, Cell, 78:915-918 (1994); Garthwaite and Boulton, Annu. Rev. Physiol, 57:683-706(1995)). NO is produced from arginine by NOS in almost all cell types. A group of three chromosomal genes, giving rise to numerous isoforms of NOS, have been cloned from mammalian cells (Knowles and Moncada, Biochem. J., 298:249-259 (1994); Wang and Marsden, Adv. Pharmacol, 34:71-90 (1995)), and recently a Drosophila NOS gene, whose coding structure resembles the gene for the mammalian neuronal isoform, has been isolated (Regulski and Tully, Proc. Natl. Acad. Sci. USA, 92:9072-9076 (1995)).
Cell division and subsequent programmed cell death in imaginal discs of Drosophila larvae determine the final size of organs and structures of the adult fly. Results described herein show that NO is involved in controlling the size of body structures during Drosophila development. These results demonstrate that NOS is expressed at high levels in developing imaginal discs. Inhibition of NOS in larvae causes hypertrophy of organs and their segments in adult flies, whereas ectopic expression of NOS in larvae has the opposite effect. Blocking apoptosis in eye imaginal discs unmasks surplus cell proliferation and results in an increase in the number of ommatidia and component cells of individual ommatidia. These results demonstrate the activity of NO as an antiproliferative agent during Drosophila development, controlling the balance between cell proliferation and cell differentiation. Moreover, results shown here demonstrate that NO acts as a crucial regulator of hematopoiesis after bone marrow (BM) transplantation. NO regulates the maturation of both the erythroid and myeloid lineages. These data demonstrate that manipulations of NOS activity and NO levels during hematopoiesis can be used to alter (enhance or reduce) blood cell production. This is useful for preventive and therapeutic intervention.
During Drosophila development, the structure, size, and shape of most of the organs of the adult fly are determined in the imaginal structures of the larvae (Cohen, Imaginal disc development, in The Development of Drosophila melanogaster, M. Bate and A. Martinez-Afias, eds. (Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y.), 747-841 (1993); Fristrom and Fristrom, The metamorphic development of the adult epidermis, in The Development of Drosophila melanogaster, M. Bate and A. Martinez-Afias, eds. (Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y.), 843-897 (1993)). Imaginal discs, specialized groups of undifferentiated epithelial cells that are recruited during embryogenesis, are formed in the first larval instar as integuments of the larval epidermis. Disc cells divide rapidly throughout the larval development and cease proliferating at the end of the third instar period.
In leg, wing, and haltere discs, progression through the cell cycle stops in G2 phase 3-4 hours before puparium formation. It resumes 15-18 hours later (12-14 hours after pupariation) and then stops again in a defined spatial pattern after 12-14 hours (10-14 hours of pupal development) (Fain and Stevens, Dev. Biol., 92:247-258 (1982); Graves and Schubiger, Dev. Biol., 93:104-110 (1982); Schubiger and Palka, Dev. Biol., 123:145-153 (1987)). Although most of the dividing cells in the late larvae and in the early pupae are already committed to their adult fate, they do not develop a fully differentiated phenotype until growth arrest is firmly established. Thus, cell proliferation is temporally separated from cell differentiation, which takes place later during metamorphosis. Experiments with transplanted imaginal discs suggest that cessation of cell proliferation in these structures is controlled by mechanisms that, while intrinsic to the disc, are not completely cell-autonomous (Bryant and Schmidt, J. Cell Sci., Suppl. 13:169-189 (1990); Cohen, Imaginal disc development, in The Development of Drosophila melanogaster, M. Bate and A. Martinez-Afias, eds. (Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y.), 747-841 (1993)). The signaling pathways that control coordinated temporary growth arrest in larvae and pupae and subsequent terminal growth arrest in pupae and adults are not known, but they probably involve intercellular and intracellular second messenger molecules which have not yet been identified.
Transformation of imaginal precursors in adult structures during fly metamorphosis involves transition from cell proliferation to cell differentiation. Cessation of cell division is a necessary, although not sufficient, condition for cell differentiation to proceed. A temporary cytostasis occurs at the end of the larval period, and permanent arrest of cell division occurs during pupal development. NO, a diffusible messenger molecule, is capable of efficiently blocking cell division. Induction of NOS initiates a switch to growth arrest prior to differentiation of cultured neuronal cells (Peunova and Enikolopov, Nature, 375:68-73 (1995)). Thus, NOS can act as a permissive factor, making the further development of the fully differentiated phenotype possible. Results described herein show that NOS acts as an antiproliferative agent during normal Drosophila development, indicating that NO is an important growth regulator in the intact developing organism.
Throughout larval development, there is a gradual and spatially-specific accumulation of NADPH-diaphorase activity in developing imaginal discs, reflecting an increase in overall NOS content. At the time temporary cytostasis is being established in imaginal discs, NADPH-diaphorase staining becomes particularly intense, and it gradually decreases during prepupal and pupal development. Besides the imaginal discs, other structures with intense NADPH-diaphorase staining include imaginal rings, histoblasts and the brain. These structures undergo radical changes during metamorphosis before giving rise to adult organs. Their development includes periods of rapid cell division alternating with periods of cytostasis, and thus must employ mechanisms for coordinated cessation of DNA synthesis and cell division in a spatially defined pattern. Since NO can prevent cell division and can diffuse and act within a limited volume, the ability of NO to act to induce coordinated growth arrest during Drosophila development was considered. Indeed, if NO actively exerts its antiproliferative activity during the development of imaginal discs, then inhibition of NOS before the temporary cytostasis is established at the end of the larval period could lead to the reversal of the arrest of cell division and induce additional divisions, which in turn could lead to increased size of structures of the body of the adult fly. Conversely, excessive or ectopic-production of NO in larvae could cause premature cessation of cell division and lead to a reduction in the size of the structures in the adults.
Both predictions were confirmed in experiments described herein, in which NOS activity was manipulated in the developing fly. NOS inhibition in larvae caused an increase in the number of cells in some parts of the adult body and an increase in their size, whereas ectopic expression of the NOS transgene during development caused a decrease in the number of cells in some structures in the adult and a decrease in their size, probably by partial fusion and reduction. In the developing leg, the segments that were most often affected when NOS activity was inhibited and the segments that were most often affected when the activity was ectopically induced were nonoverlapping and complementary. Most importantly, their distribution matched the distribution of NOS in the imaginal discs, thereby supporting the hypothesis that NO plays a causative role in growth arrest in normal development.
The antiproliferative properties of NO suggest that NOS acts in development through its influence on DNA synthesis and cell division. The results described herein with BrdU incorporation in leg discs with elevated and diminished production of NO corroborate this position and suggest a direct link between synthesis of NO, number of S-phase cells, and the final size of the organ. In accordance with this idea, in many instances no BrdU incorporation was observed in regions highly enriched in NOS. The mechanisms for the NO-mediated arrest of the cell cycle (both temporary and terminal) are not clear, but they likely involve the conventional cellular machinery for growth arrest, e.g., cell cycle-dependent kinases and their inhibitors. Consistent with this, changes in expression of these proteins were observed when cultured cells were treated with NO. An intriguing feature of imaginal disc cells is that they stop dividing and accumulate in G2 phase in the late third instar, preceding the period of temporary cytostasis (Fain and Stevens, Dev. Biol., 92:247-258 (1982); Graves and Schubiger, Dev. Biol., 93:104110 (1982); Schubiger and Palka, Dev. Biol., 123:145-153 (1987)). This parallels a tendency of NO-treated (Peunova and Enikolopov, Nature, 375:68-73 (1995)) and NGF-treated (Buchkovich and Ziff, Mol. Biol. Cell, 5:225-241 (1994)) PC12 cells to accumulate in G2 phase. Interestingly, imaginal discs are released from the G2 block and reenter S phase 12-15 hours after pupariation, at the time when diaphorase staining is diminished to low levels in adult flies. These correlations between imaginal discs cells and NO-treated cells support the idea that NO can be a major inducer of cytostasis in the cells of imaginal discs in the prepupal stage.
The final number of cells in an organ or a segment is determined both by cell multiplication and cell death, which the forming structures of the fly undergo as a normal step in development (especially at the late stages of pupal development). Results described herein indicate that the changes in the size of the leg segments after manipulation of NOS activity correlated directly with the changes in DNA synthesis and the number of dividing cells. Furthermore, no significant changes in apoptosis were detected in the larval and prepupal leg discs after inhibition or ectopic expression of NOS, compared with the control discs, when cell death was monitored by acridine-orange staining or by the TUNEL assay. This suggests that it is cell multiplication, rather than changes in programmed cell death that leads to the changes in the size of the appendage.
On the other hand, apoptotic death may conceal excessive cell proliferation in other developing organs. The effect of the absence of programmed cell death on potential excessive cell proliferation was also assessed. Transgenic flies were used in which programmed cell death in the developing eye was suppressed by recombinant p35, an inhibitor of apoptosis, to reveal excessive proliferation after NOS inhibition. Under these circumstances, several cell types and structures are overrepresented, the most noticeable change being an overall increase of the size of the eye due to the increased number of ommatidia. In addition, other cell types (e.g., secondary and tertiary pigment cells, cone cells, and cells of the bristles) proliferated after NOS inhibition to levels higher that those achieved by blocking apoptosis by p35 (Hay et al, Dev., 120:2121-2129 (1994)). These data demonstrate that the removal of suppressive influence of NO leads to an increase in the size of the adult organ, unless this effect is masked by programmed cell death, and indicate that final cell number in the adult organ is under dual control by both cell proliferation and programmed cell death. Furthermore, these data provide independent support for the hypothesis that NO directly regulates cell number during development.
After inhibition of NOS with either of two structurally unrelated compounds, excessive growth was observed in most of the structures of the adult flies that derive from imaginal discs and histoblasts, to varying extents for different organs. The most obvious changes were observed in the segments of the legs whose primordia showed the highest levels of NOS. There did not appear to be any substantial number of instances in which a duplication of a larger structure (for example, segments of the legs or wings) occurred. This indicates that extra proliferation of cells under the influence of NOS inhibitors occurs after the developmental fate is determined for most of the cells in the imaginal discs. This suggests that in most cases NO may be more important for the induction of growth arrest and subsequent differentiation of already committed cells than for the developmental commitment and establishment of the cell identity in the embryo or larvae.
Only some of the axes of the developing structures were affected by manipulations of the NOS activity. For instance, in developing legs only the anteroposterior and the dorsoventral axes, but not the proximodistal axis, were affected by inhibition of NO production. In contrast, when NOS was ectopically expressed, only the proximodistal axis was affected. These results suggest that a gradient of NO may be involved in the process of establishing the polarity of the axes of the developing organ.
Thus these results demonstrate that inhibition of NOS in larvae leads to enlargement of organs in adults and, conversely, that ectopic expression of NOS in larvae leads to a reduction in the size of organs in adults. Also, the distribution of affected segments in the adult leg corresponds to the distribution of NOS in the larvae, and the changes in segment size can be directly correlated to changes in DNA synthesis in imaginal discs after manipulations of NOS activity. The increased cell proliferation that occurs in response to NOS inhibition is masked in some structures by programmed cell death, and it can be revealed by suppressing apoptosis. Taken together, these results demonstrate that activation of NOS is a crucial step in Drosophila development. They confirm that NO acts as an antiproliferative agent during cell differentiation and organism development and controls the cell number in an intact developing organism.
NOS expression can be induced to high levels in a large number of tissues and cell types by appropriate stimulation (Bredt and Snyder, Annu. Rev. Biochem., 63:175-195 (1994); Forstermann et al., Adv. Pharmacol., 34:171186 (1995)). In most cases, the pattern of NOS distribution in a developing organism differs strongly from the distribution in the adult organism. Furthermore, transient elevation of NOS expression in a given tissue often coincides with the cessation of division of committed precursor cells. The developing mammalian brain provides an especially apt demonstration of this (Bredt and Snyder, Neuron, 13:301-313 (1994); Blottner et al., Histochem. J., 27:785-811 (1995)). A strong elevation of NOS activity in the developing cerebral cortical plate and hippocampus at days 15-19 of prenatal development correlates with the timecourse of cessation of precursor cells proliferation, tight growth arrest, and cell differentiation; notably, NOS activity goes down after the proliferation of committed neuronal precursors is completed. NOS levels are also transiently increased in developing lungs, bones, blood vessels, and nervous system (Blottner et al., Histochem. J., 27:785-811 (1995); Collin-Osdoby et al., J. Cell Biochem., 57:399-408 (1995); Cramer et al., J Comp. Neurol., 353:306-316 (1995); Shaul, Adv. Pediatr., 42:367-414 (1995); Wetts et al., Dev. Dyn., 202:215-228 (1995)). Elsewhere, NOS activity is greatly elevated in regenerating tissues when cessation of cell division is crucial for prevention of the unregulated growth (Roscams et al., Neuron, 13:289-2Y9 (1994); Blottner et al., Histochem. J., 27:785-811 (1995); Decker and Obolenskaya, J. Gastroenterol. Hepatol., 10 Suppl 1:2-7 (1995); Hortelano et al., Hepat. 21:776-786 (1995)). In all these cases, a transient elevation of NOS activity might trigger a switch from proliferation to growth arrest and differentiation, thus contributing to the proper morphogenesis of the tissue and the organ.
Results described herein support the position that production of NO is required during embryonic development and during tissue regeneration in the adult organism for the proper control of cell proliferation. The antiproliferative properties of NO are particularly important in situations in which terminal differentiation of committed cells is temporally separated from cell proliferation and is strictly dependent on cessation of cell division. Given the multiplicity of the NOS isoforms and their overlapping tissue distribution, it is conceivable that any group of cells in the embryo and fetus can be exposed to NO action. Furthermore, recent data showing that NO can be transferred within the organism by hemoglobin (Jia et al., Nature, 380:221226 (1996)) raise the possibility that a developing mammalian embryo can be also supplied with NO exogenously by the mother.
NO is a readily diffusible molecule, and it may therefore exert its antiproliferative properties not only in the cell that produces it but in the neighboring cells as well (Gally et al., Proc. Natl. Acad. Sci. USA, 87:3547-3551 (1990)). This property is important when one considers mechanisms for the coordinated development of a group of neighboring cells committed to form a particular structure. These cells have to generate an intrinsic signal that tells them to stop dividing in a coordinated fashion after they have reached a certain number. This cooperation and coordination is achieved in many instances by tightly controlled paracrine regulation, which involves signaling between adjacent cells via gap junctions or secreted proteins. Results described herein show that yet another way of coordinating developmental decisions in groups of cells is by diffusible antiproliferative second messenger molecules, which can spread without a need for surface receptors or specialized systems for secretion and exert their influence within a limited domain. An efficient source of readily diffuisible molecules may induce synchronized changes in the adjacent cells within a limited volume of a tissue. Moreover, several adjacent cells producing easily diffusible antiproliferative messenger molecules may share the total pool of these molecules produced by the neighbors as well as by themselves. If a particular threshold level of a signal is needed to initiate a signaling chain that eventually leads to growth arrest, then the cells in this group could stop dividing when a certain number of cells and, therefore, a certain local concentration of messenger molecules, is reached. In this way, by organizing groups of cells in functional clusters and coordinating their decisions on proliferation and differentiation, No instruct the developing structures to terminate their growth when they attain the appropriate size and shape, and, thus, participate in tissue and organ morphogenesis.
As also described herein, the role of NO in hematopoiesis was examined. To demonstrate the presence of NOS in the bone marrow (BM) cells, BM from adult mice was tested for the NDPH-diaphorase activity of NOS (which reflects the distribution of the total enzyme activity in a tissue). It was found that BM contains a substantial proportion of cells (up to 12%) with strong diaphorase staining. The morphology of the NADPH-diaphorase cells suggests that they are largely of the granulocyte-macrophage lineage at different stages of differentiation. This is in accordance with numerous data showing that NOS is present in the cells of the myeloid lineage, and can be induced to high levels by appropriate stimulation.
A mouse model of syngeneic BM transfer was used to evaluate the role of NO in hematopoiesis. Mice were irradiated to inhibit hematopoiesis in the recipient animal, BM was transplanted from syngeneic animals, and the animals were treated with specific NOS inhibitors. This procedure permits the proliferation, differentiation and survival of only the transplanted cells. To study the changes in hematopoiesis introduced by NOS inhibitors, the colonies in the spleen were monitored to test the differentiation of erythroid cells, and the formation of colonies on the membranes placed in the peritoneal cavity of the recipients were monitored to test the differentiation of cells of the granulocyte-macrophage lineage. The role of NO on hematopoiesis was tested by injecting the animals with the specific and structurally unrelated NOS inhibitors L-nitroarginine methyl ester (L-NAME), and 2-ethyl-2-thiopseudourea (ETU). The inactive enantiomer D-NAME was used as a control. Animals were sacrificed and the number and composition of colonies in the spleen (reflecting the cells which have undergone erythroid differentiation) and colonies on the membranes (reflecting the cells that have undergone myeloid differentiation) were studied.
Taken together, the results of these studies indicate that NO modulates hematopoiesis after BM transplantation. This confirms the role of NO as a major regulatory factor in the organism controlling the balance between proliferation and differentiation. This also shows that manipulation of NO levels may be used for therapeutic intervention to increase the number of undifferentiated hematopoietic cells after BM transplantation; change the ratio of cells undergoing erythroid or myeloid differentiation; and interfere or suppress graft-versus-host disease, which is a major cause of mortality in patients undergoing BM transplantation.
Most of the tissues and organs in the adult organism are constantly undergoing regeneration and renovation, going through phases of rapid proliferation, determination, growth arrest, differentiation, and often, programmed cell death. Many human diseases are caused by improper or incomplete differentiation steps, resulting in the loss of function of a particular tissue or organ. This suggests that these diseases can be treated, and, furthermore, proper function of the affected tissues and organs can be restored by targeting and manipulating cell and tissue differentiation.
This work described herein, demonstrating the role of NO in cell proliferation and differentiation in an organism, provides for various therapeutic applications in humans and other mammals. In particular, this NO-based approach can be focused on renewable and regenerating tissues, such as blood, bone, skin, and digestive epithelium. Additionally, a similar strategy can be used to repopulate organs with normally nondividing cells such as muscle and nerve cells.
The work described herein can also be used to enhance gene therapy methods. For example, NOS can be used to drive a population of cells into the S phase wherein the cells are replicating. As known in the art, replicating cells are more responsive to gene therapy methods (e.g., introduction of genes via live vectors) than non-replicating cells. Thus, the present invention provides for a method of converting cells into a state which renders the cells more receptive to gene therapy methods, wherein the cells are contacted with a NO inhibitor (e.g., NOS inhibitor). Conversely, the present invention provides for a method of converting cells into a state which renders the cells resistant to gene therapy methods. That is, the present invention provides for a method of converting cells into a state which renders the cells more resistant to gene therapy methods, wherein the cells are contacted with NO and/or a NO enhancer (e.g., NOS enhancer).
The results of work described herein support the ability of NO to act as a crucial regulator of hematopoiesis after bone marrow transplantation (BMT). NO regulates maturation of both erythroid and myeloid cell lineages. By interfering with NO production in the recipient animal after BMT, the number of undifferentiated stem and blast cells which are then capable of further differentiation along the erythroid or myeloid lineages can be dramatically increased. The blast cells enrichment reaches 80-fold for the myeloid lineage, and 20-fold for the erythroid lineage. The data described herein demonstrates that manipulations of NOS activity and NO levels during hematopoiesis can be used for therapeutic purposes to influence self renewal and differentiation of hematopoietic stem cells, and to replace damaged or defective cells. Areas of application include enhancement of blood cell and myeloid cell formation following high dose chemotherapy in cancer treatment; improved engraftment following bone marrow or stem cell transplantations, and gene therapy; stem cell therapy by amplifying the undifferentiated cells of erythroid and myeloid lineages and applying appropriate factors to induce terminal differentiation; and regulation of formation of various blood cell components for treating hematological and autoimmune disorders.
The data also shows that changing the levels of NO production interferes with osteoblast and chondrocyte differentiation. These results show that manipulation of NO production can regulate growth and differentiation of osteoblasts, chondrocytes, or mesenchymal stem cells. This can be used for amplification and further differentiation of cells in the injured tissue, or for cell implants (in combination with biocompatible carriers, if necessary). Thus, an NO-based approach can be used for regeneration therapy of the damaged tissue, post injury repair, age related diseases such as osteoporosis and osteoarthritis, and for reconstituting marrow stroma following high dose cancer chemotherapy.
In addition, the data shows that changing the levels of NO production interferes with keratinocyte differentiation. The results described herein demonstrate that regulation of NO production can be used when increased proliferation and subsequent differentiation of skin tissue is required (e.g., during burns and wound healing). Furthermore, NO can be used to control disorders caused by hyperproliferation of keratinocytes during psoriasis. Yet another potential application is to use NO-based preparations as exfoliant agents in cosmetic therapy.
NO has been shown to act as a regulator of cell differentiation in neuronal cells. It has been demonstrated that NO regulates brain development in animals and contributes to controlling the size of the brain in intact animals.
It has also been demonstrated that in certain contexts NO mediates the survival effects of growth factors by activating an antiapoptitic program and can protect neuronal cells from death. Combined, these studies of the role of NO in neurons suggest that NO may be used to control proliferation and subsequent differentiation of nerve cells in replacement therapy after neurodegenerative disorders caused by aging (e.g., Alzheimer""s or Parkinson""s), stroke, or trauma.
NO is actively produced in smooth muscle cells of the blood vessels and is subject to complex physiological regulation. These cells are highly susceptible to suppression of DNA synthesis by NO. The very strong antiproliferative activity of NO can be used for inhibition of smooth muscle cells proliferation and neointima formation for treatment of restenosis following angioplasty.
In addition, NO-based therapy has application for treatment of ailments characterized by destruction of specific sets of cells. This includes hepatocyte regeneration after toxic injury of the liver, treatment of reproductive system disorders, and administration of differentiated pancreatic tissue for treatment of type 1 diabetes.
The methods of the present invention can be carried out in vivo or ex vivo. Administration of the NO inhibitor, NO enhancer and/or agent which induces differentiation can performed using various delivery systems known in the art. The routes of administration include intradermal, transdermal, intramuscular, intraperitoneal, intravenous, subcutaneous, oral, epidural and intranasal routes. Any other convenient route of administration can be used such as, for example, infusion or bolus injection, or absorption through epithelial or mucocutaneous linings. In addition, the NO inhibitor, NO enhancer and/or agent which induces differentiation can be administered with other components or biologically active agents, such as adjuvants, pharmaceutically acceptable surfactants, excipients, carriers diluents and vehicles. Administration can be systemic or local, e.g., direct injection at the site containing the cells to be targeted. In the embodiment, in which the NO inhibitor, NO enhancer and/or agent which induces differentiation are protein or peptides, they can be administered by in vivo expression of genes or polynucleotides encoding such into a mammalian subject. Several expression systems, such as live vectors, are available commercially or can be reproduced according to recombinant DNA techniques for use in the present invention.
The amount of NO inhibitor, NO enhancer and/or agent which for use in the present invention which will be effective in the treatment of the particular disorder or condition will depend on the nature of the disorder or condition, and can be determined by standard clinical techniques. The precise dose to be employed in the formulation will also depend on the route of administration and the seriousness of the disease or disorder, and should be decided according to the judgement of the practitioner and each patient""s circumstances. For example, the amount of NO inhibitor(s) for use in the methods of the present invention can be from about 1 mg/kg body weight to about 1000 mg/kg body weight, from about 5 mg/kg body weight to about 500 mg/kg body weight, and from about 25 mg/kg body weight to about 100 mg/kg body weight. In one embodiment, about 25 mg/kg body weight to about 1000 mg/kg body weight L-NAME and/or about 1 mg/kg body weight to about 100 mg/kg body weight can be used in the methods of the present invention. In a particular embodiment, about 300 mg/kg body weight L-NAME is used in combination with about 30 mg/kg body weight ETU in the methods of the present invention.